Earlier this year, students working about 30 feet (9 meters) below the surface found the remains of a gourd that probably was used as a canteen by an ancient hunter about 8,000 or 9,000 years ago, according to Gifford.

Archaeologists have been recovering primitive relics from the spring since 1977, when divers found the remains of a large, now extinct tortoise and a sharpened stake that may have been used by a hungry hunter to kill the animal 12,000 years ago.

In 1986, Gifford and his colleagues recovered a skull with brain tissue from what he thinks was an ancient burial in shallow water near the spring. He continues to work with DNA samples to determine the date of the find.

Gifford and other archaeologists found more from the tortoise this past July, along with the slaughtered remains of a giant ground sloth.

The discovery of the sloth's bones, Gifford said, could indicate that Little Salt Spring was a sort of ancient butcher shop where hunters often killed their prey and prepared meat when this was dry land.

These remains come from the earliest known period of human activity in the Western Hemisphere, said Gifford, who has received funding for his work from the National Geographic Society's Committee for Research and Exploration. (National Geographic News is owned by the National Geographic Society.)

"This is a warehouse of environmental, natural, historical, and archaeological remains in a very, very well preserved environment," said Roger Smith, Florida's state underwater archaeologist.

"That's why it's a world-class site. I would call it a portal back into time."